Originally Posted by Brian B-P
The gelcoat is just the first layer sprayed into the mould; it can just be skipped, so non-coloured resin is visible on the exterior of the resulting shell... although understandably ETI isn't willing to do that.
I'm not so sure it can be skipped with the production process that ETI uses. If you're basing your statement on the Corvette that uses a different production process (compress molded fiberglass) than Escape trailers.
For Escape trailers the interior of the mold is gelcoat. The smooth gelcoat in the mold is then waxed with a mold released. The gelcoat is then sprayed on top of that. That provides a smooth surface that allows the trailer shell to slip easily out of the mold. I'm not so sure the raw fiberglass would release as cleanly from the mold. The mold release agent might also wick up the glass fibers reducing the effectiveness of the mold release and possibly weakening the fiberglass.
The red gelcoat on the mold contrasts against the white gelcoat of the trailer so the person applying the gelcoat can see if there are any thin areas of the gelcoat. The white gelcoat contrasts against the light blue coloring in the fiberglass resin again giving the applicator a guide to proper thickness. All of those 'cues' are lost if you tried to apply the fiberglass directly to the mold without the layer of gelcoat.
While Escape trailers aren't built to aircraft tolerances, losing the 1/8 inch or so of gelcoat off the mold would change the dimensions of the interior of the trailer, so all interior parts cut from templates would fit slightly looser on the interior of the trailer than they should.
The gelcoat provides a protection from the elements for the fiberglass. Without gelcoat or paint the bare fiberglass fibers could wick in moisture while the trailer is outdoors between production steps.
Without Gelcoat the bottom of the trailer would be raw fiberglass. The entire body of the trailer would have to be removed from the frame to properly finish the the raw fiberglass bottom and protect if from the elements.
Gelcoat can be painted over so there is no advantage to producing the trailer without gelcoat to begin with. Raw fiberglass is going to require more paint layers to prevent the glass pattern from showing through the paint so not having the gelcoat is actually a disadvantage.